The codex itself outlines the steps required in order to complete the treasure hunt. The walkthrough outlines each step for each clue.

Note: If you are not interested in following every step, simply complete the steps from #4 onwards (lighting the torches). Finding a clue will update the codex temporarily however once the treasure hunt is complete, the codex will disappear. It can be picked up afterwards, however.

The first clue is the first line of the codex which points to #12 in the subsequent list: "Beyond Andraste's Mercy, a hundred steps to revelation."

Andraste's Mercy is a landmark in the Emerald Graves northwest of the codex, marked with an "X". The next clue is found by searching northwest of the "X", between the outer wall of Villa Maurel and a large tree (look north from the easternmost point of the wall as indicated on the map).

This will give you the second clue which points to #3 on the list: "Arching above outstretched wings. Even stone can rise."

Follow the road northwest towards The Lion's Pavilion. You will come to a gap in the rocks next to a statue of an owl. This is northwest of the Silver Falls landmark on the map.

Climb up the rocks to reveal a search that will give you the next clue, pointing to #9 on the list: "Dragonslayers, four at the northwest, two from the northeast, three from the southeast."

This is a reference to the statue inside the Lion's Pavilion, therefore keep on the road until you reach the pavilion.

At this point, the clue can be misleading. Where it says "northwest", it isn't referring to the compass direction on the map. Instead, face the statue inside the pavilion and use the back wall as "north".

Then, light the torches in accordance with the codex—northwest torch four times, northeast torch twice and southeast torch three times. If done correctly all four torches and the central brazier will light up revealing the next clue which is #20 on the list: "At the first breath of sighs."

Head north to the river and an area called Rush of Sighs. Follow the river northwest to the waterfall. A search here will reveal the last clue—#14: "An upward pointing finger, there your heart lies."

Head northeast to Southfinger Tower and search on the southwest side. Note you don't need to access the tower itself, the search area is on the ground below. Be wary of the giants in the area as they can be pulled into the fight that's about to happen. Once you loot the Misshapen Child's Doll two lesser shades and one elite despair demon called "Treasure" (maximum level 19).